The mounting and use of an optical element, e.g., an optically active surface, in a micromechanical component poses special challenges to the packaging of the micromechanical component, which do not present themselves when a microelectrical and/or a purely micromechanical element is used in the micromechanical component. Microelectrical and/or purely micromechanical elements such as sensors or mechanical actuators, for example, usually have only electrical interfaces. This simplifies a complete encapsulation of the microelectrical and/or purely micromechanical elements at the wafer level. The encapsulation can take place in a clean or super-clean environment. In addition, the complete encapsulation of a microelectronic and/or purely micromechanical element at the wafer level is able to be implemented in a relatively cost-effective manner because processes run in parallel. Following the encapsulation, the microelectronic and/or purely micromechanical elements can be separated, cleaned and/or processed further in a normal, clean environment. For instance, an installation inside a chip housing, the development of an electrical contacting and/or an insertion into a system take(s) place.
The use of an optical element in a micromechanical component inside a protective housing usually requires optical radiation to be coupled in and/or out. The incoupling and/or decoupling of optical radiation frequently takes place via an incident light window made of a light-transmitting material having a refractive index not equal to 1. For example, such an incident light window is formed in the encapsulation of an active surface from at least one glass wafer, since glass wafers have suitable optical properties such as transparency, roughness and planarity. An encapsulation of the optical element with the aid of a glass wafer is possible at a wafer level as well.
FIG. 1 shows a schematic illustration of a first conventional micromechanical component having an optically active surface. Conventional micromechanical component 10 has a reflective surface of a reflective plate 12 as optically active area. To protect against environmental effects, reflective plate 12 is situated inside a housing formed by a frame part 14, an upper cover 16, and a lower cover 18. Upper cover 16 is at least partially made of a light-transmitting material. The housing formed by components 14 through 18 may have an airtight design, for instance.
Reflective plate 12 is joined to the housing formed by components 14 through 18 via at least one spring element 20. Via an electrostatic and/or magnetic drive, reflective plate 12 is able to be rotated about an axis of rotation running along the longitudinal axis of spring element 20. Dashed lines 12a show possible positions of reflective plate 12 with respect to covers 16 and 18.
A beam of light 22 incident on the boundary surfaces of upper cover 16 is partially reflected. The transmitted component of incident beam of light 22 strikes reflective plate 12, which directs it as a deflected beam of light 24 to an image plane 26. Depending on the position of reflective plate 12, deflected beam of light 24 strikes various points of image plane 26. Beam of light 28 reflected at the boundary surfaces of upper cover 16 may at least partially also strike image plane 26 and thus lead to an interference reflex on image plane 26. If upper cover 16 has a large reflection coefficient for the angle of incidence of incident beam of light 22, then the interference reflex may have a relatively high light intensity. The interference reflex, unlike beam of light 24 deflected by reflective plate 12, is not variable in its location.
One may—for preventing interference reflexes—dispense with the use of a housing which completely surrounds reflective plate 12. In this case, however, a reflective plate 12 is no longer protected from environmental influences. In addition, a reflective plate 12 not protected by a housing is often more difficult to separate and/or able to be installed in a device only with more difficulty. More specifically, in such a case it is frequently impossible to utilize standard processes for the separation or the installation.
FIG. 2 shows a schematic illustration of a second conventional micromechanical component having an optically active surface.
Illustrated micromechanical component 30 includes the already described components 12, 14, 18, and 20. In addition, micromechanical component 30 has an upper glass cover 32 made up of a glass cover plate 34 and a side plate 36. Glass cover plate 34 on which an incident beam of light 22 impinges is aligned at an angle with respect to a center position of reflective plate 12. Beam of light 28 reflected at the boundary surfaces of cover plate 34 is therefore not deflected to image plane 26 of reflective plate 12. This prevents interference reflexes at image plane 26.
However, upper glass cover 32 is difficult to realize at the wafer level. Producing a glass wafer having sloped surfaces is relatively work-intensive and thus relatively expensive. Especially the polishing of the sloped surfaces is frequently not able to be accomplished in satisfactory manner, so that the sloped surfaces have high transparency and very low roughness.